Help! Need a vegetable/salad side to cut through the heaviness of the rest of my dinner party menu - any suggestions?

Your menu sounds delicious! If it were me I'd go with something simple and citrusy and raw for contrast - perhaps raw fennel and orange salad with an orange vinaigrette and black olives. Good luck with your dinner.

I've been really happy with making side Mexican fruit salad.
And since you mention Chorizo...it might pare well.

Just take this as a sketch:
Watermelon, Mandarine Orange Slices, Cucumber cubes, Cherry Tomato, Red Onion, Jicama cut into sticks. Green Chile pepper.

Okay...there's a lot of different fruits and veggies in that mix. Add Cilantro roots chopped (or parsley of you have a dinner party with cilantro haters).

Now, for a addition add Feta Cheese..or Mexican crumbly cheese.
And for a dressing...lime juice/olive oil/oregano/garlic..cumin, a bit of salt and really good crunchy salt on the surface to finish.

A simple green salad with vinaigrette. You could also do a salad of thinly sliced beets with goat cheese.

This lemon-caper-mustard salad dressing from April Bloomfield is the very definition of bracing:
https://food52.com/blog/3186-april-bloomfield-s-lemon-caper-dressing
Simply tossed with some good crisp lettuce it's tart, pungent, and a great contrast to rich and sweet foods. The suggested addition of a little bit of something fatty to the salad is nice but not necessary, particularly if your other dishes are rich. As a mostly vegetarian, I often go with a little bit of avocado.

or Sara's collards!

https://food52.com/recipes/26383-zesty-and-zippy-tangled-collards

Not to be boring, but since you're already serving butter/cream sauce and a salad with a rich tahini dressing, I wouldn't add another rich, complex flavor, or cheese, etc. I'd probably just do some wild rice to soak up all those sauces. If you want another salad, just a simple one to cut the richness (e.g., butter lettuce w/ sherry vinaigrette - scatter some toasted sliced almonds if you want to gussy it up.) Otherwise perhaps spinach sauteed with garlic.

Make a cool refreshing salad of sliced or chunk-cut cucumbers, a melon if you can find a ripe one (or pineapple), spiked with some onion, garlic, cilantro, then light (or no) vinaigrette.

This may be consider lowbrow by some but would you consider a wedge? Crisp iceburg, with some alved cherry tomatoes, thinly sliced red onion that has been soaked in water and patted dry, maybe a smattering of blue cheese and bacon crumbles, toasted nuts, and then just a reduced balsamic drizzle. You can assemble in advance and store them in the fridge - cold and crunchy to balance a lot of warm and rich stuff.
We like them anyhow ....

Two recommendations that could offset the richness of your delicious-sounding menu:

April Bloomfield's Carrot, Avocado and Orange Salad is lovely with vibrant, fresh flavors. I have also made this subbing parsley for cilantro: https://food52.com/recipes/26388-carrot-avocado-and-orange-salad

Or for a totally different dish, I think that Queen Sashy's Spice Merchant Cauliflower Couscous would be a delicious accompaniment to the chicken and the chickpea/squash salad: https://food52.com/recipes/21165-spice-merchant-cauliflower-couscous

My recommendation is a pear and blue cheese salad like this one,
http://www.foodnetwork.com/recipes/food-network-kitchens/pear-and-blue-cheese-salad-recipe.html

My favorite salad and I don't play favorites very often.